Phagocytosis

PHAGOCYTOSIS.,INFLAMMATION

1. GOOD MORNING

2. PHAGOCYTOSIS Dr.Mahima Tyagi P.G.1 st year

3. CONTENTS Definiton Phagocytic cells Stages of phagocytosis Metchnikoff theory Chemical mediators of inflammation Diseases Conclusion Referrences

4. Phagocytosis is defined as process of engulfment of solid particulate material by the cells (cell-eating).The cells performing this function are called phagocytes. There are two main types of phagocytic cells. Polymorphonuclear neutrophils microphages Circulating monocytes and fixed tissue mononuclear phagocytes called as macrophages DEFINITION

5. 1.polymorphonuclear neutrophils 2.eosinophils 3.basophils 4.mononuclear-phagocyte system 5.Dendritic cells PHAGOCYTIC CELLS

6. 1.Neutrophills These cells along with basophils and eosinophils are k/a granulocytes due to presence of granules in cytoplasm. These granules may contain substances like proteases , myeloperoxidase,lysozyme,esterase,aryl sulfatase,acid and alkaline phosphatase and cationic proteins. Diameter of neutrophil ranges from 10-15µm and are actively motile.

7. These cells comprise 40-75% of circulating leucocytes and their number is increased in blood( neutrophilia ) and tissues in acute bacterial infections.These cell arise in bone marrow from stem cells . Their role in phagocytosis A)initial phagocytosis of micro organisms as they form the first line of defence in bacterial infection.

8. Neutrophils, which along with macrophages comprise the professional phagocytes, are endowed with a unique capacity to engulf and thereby eliminate pathogens and cell debris. Phagocytes are equipped with specialized receptors to recognize their targets; this complex machinery mediates internalization and initiates an assortment of degradative mechanisms that culminate in killing and disposal of the engulfed particles.

9. The steps involved are adhesion of neutrophils to vascular endothelium,emigration through the vessel wall,chemotaxis,engulfment,degranulation,killing and degradation of the foreign material. Engulfment of antigen-antibody complexes and non-microbial material.

10. Harmful effect Destruction of neutrophils is destruction of the basement membranes of glomeruli and small blood vessels.

11. 2.Eosinophills These are larger than neutrophils but are fewer in number comprising 1 to 6% of total leucocytes. Eosinophils share many structural and functional similarities with neutrophils like their production in the bone marrow, locomotion , phagocytosis,lobed nucleus and a presence of granules in the cytoplasm containing a variety of enzymes of which major basic protein and eosinophil cationic protein are most important which have bactericidal and toxic action against helminthic parasites.

12. However,granules of eosinophils are richer in MPO than neutrophils and lack lysozyme .High level of steroid hormone leads to fall in number of eosinphils and even disappereance from blood. The absolute number of eosinophils is increased in :- Allergic conditions Parasitic infections Skin diseases Certain malignant lymphomas

13. 3.Basophils The basophils comprise about 1% of circulating leucocytes and are morphologically and pharmacologically similar to mast cells of tissue. These cells contain coarse basophilic granules in the cytoplasm and a polymorphonuclear nucleus. These granules are laden with heparin and histamine.

14. Basophils and mast cells have receptors for IgE and degranulate when cross linked with antigen. The role of these cells in inflammatory are: In immediate and delayed type of hypersensitivity reactions and 2) release of histamine by IgE sensitized basophils.

15. 4.Mononuclear-Phagocyte System( Reticuloendothelial System) This cell system includes cells derived from 2 sources with common morphology,function and origin. These are as under: 1)Blood monocytes . These comprise 4-8% of circulating leucocytes. 2)Tissue macrophages. These include the following cells in different tissues.

16. Macrophages in inflammation Histiocytes which are macrophages present in connective tissues Kupffer cells which are macrophages of liver cells. Alveolar macrophages present in lungs Free and fixed ,macrophages and sinusoidal lining cells of spleen,lymph node and bone marrow. Macrophages of serous cavities Microglial cells of nervous sysytem Langerhan’s cells of skin. Dendritic cell found in lymphoid tissue .

17. The mononuclear phagocytes are the scavenger cells of the body as well as participate in immune system of the body. Their functions in inflammation are :- 1.Phagocytosis(cell eating) and pinocytosis(cell drinking) 2.Macrophages on activation by lymphokines released by T lymphocytes or by non-immunologic stimuli elaborate a variety of biologically active substances such as:

18. Proteases like collegenase and elastase which degrade colagen and elastic tissue . Plasminogen activator which activates the fibrinolytic system. Products of complement Some coagulation factors(V and thromboplastin ) which convert fibrinogen to fibrin. Chemotactic agents for other leucocytes Metabolites of arachidonic acid Growth promoting factors for fibroblasts ,blood vessels and granulocytes Cytokines like interlukin-1 and tumor necrosis factor. Oxygen –derived free radicals.

19. 5.Dendritic cells Dendritic cells are present in tissues in contact with the external environment, such as the skin (where there is a specialized dendritic cell type calledLangerhans cells) and the inner lining of the  nose,lungs,stomach and intestines. .

20. . They can also be found in an immature state in the blood. Once activated, they migrate to the lymph nodes where they interact with  Tcells  and  Bcells  to initiate and shape the adaptive immune response. At certain development stages they grow branched projections, the dendrites that give the cell its name While similar in appearance, these are distinct structures from the dendrites of  neurons.Immature dendritic cells are also called  veiled cells , as they possess large cytoplasmic 'veils' rather than dendrites

21. Process of phagocytosis has 4 steps 1.Attachment stage 2.Engulfment stage 3.Secretion(degranulation) 4.Killing or degradation

22. The phagocytic cells as well as microrganisms to be ingested have usually negatively charged surface and thus they repel each other. In order to establish a bond between bacteria and cell membrane of phagocytic cell,the micro organisms get coated with opsonins which are naturally occuring factors in serum. 1.Attachment stage( opsonisation )

23. The two main opsonins and their corresponding receptors on surface of phagocyitc cells are 1. IgG opsonin and its corresponding receptor on the surface of polymorphs and monocytes is Fc fragment of immunoglobulin. 2. C3b opsonin fragment of complement and corresponding receptor for C3b on surface of phagocytic cells.

24. The opsonised particle bound to the surface of phagocyte is ready to be engulfed.This is accomplished by formation of cytoplasmic pseudopods around the particle ,enveloping it in a phagocytic vacuole. Eventually the plasma membrane enclosing the phagocytic vacuole breaks from the cell surface so that membrane lined phagocytic vacuole lies free in the cell cytoplasm. 2.ENGULFMENT STAGE

25. The lysosomes of the cell fuse with the phagocytic vacuole and form phagolysosome or phagosome .

26. During this process,the preformed granule-stored products of PMN’s are discharged or secreted into the phagosome and the extracellular enviornment . In particular ,the specific or secondary granules of PMN’s are discharged( e.g.lysosomes )while the azurophilic granules are fused with phagosomes .. 3.SECRETION (DEGRANULATION)STAGE

27. . Besides the discharge of profound granules,mononuclear phagocytes synthesise and secrete certain enzymes(e.g. interlukin2 and6,TNF), arachidonic acid metabolites( e.g.prostaglandins,leukotrines,platelet activating factor) and oxygen metabolites ( e.g.superoxide oxygen,H2O2,hypochlorus acid).

28. Stage of killing and digestion of microrganism completing the role of phagocytes as scavenger cells. The microrganisms after being killed by anti bacterial substances are degraded by hydrolytic enzymes. 4. DEGRADATION STAGE

29. The antimicrobial agents act by either of the following mechanisms. Oxygen –dependent bactericidal mechanism . Oxygen –independent bactericidal mechanism Nitric oxide mechanism

30. An important mechanism of microbicidal killing is by the production of reactive oxygen metabolites (O2,H2O2,OH’,HOCl,HOI,HOBr) A phase of increased oxygen consumption(respiratory burst’)by activated phagoctyic leukocytes requires the essential presence of NADPH oxidase. 1.Oxygen –dependent bactericidal mechanism

31. NADPH- oxidase present in cell membrane of phagosome reduces oxygen to superoxide ion.(O’2) .2O2 NADPH oxidase 2O’2 NADPH NADP+ H+

32. Superoxide is subsequently converted into H2O2which has bactericidal properties: 2O’2+2H+ H2O2 This type of bactericidal activity is carried out either via enzyme myeloperoxidase(MPO) present in the granules of neutrophils and monocytes ,or independent of enzyme MPO :-

33. A)MPO-dependent killing(H2O2-MPO-halide system). In this mechanism,enzyme MPO acts on H2O2 in the presence of halides ( chloride,iodide,bromide ) to form hypohalous acid which is more potent antibacterial agent than H2O2. MPO H2O2 HOCl+H2O Cl ’, Br’,I ’ ( hypochlorus acid)

34. B)MPO-independent killing Mature macrophages lack the enzyme MPO and they carry out bactericidal activity by producing OH ions and superoxide singlet oxygen (O’) from H2O2in presence of O’2(Haber-Weiss reaction) or in the presence of Fe++(Fenton reaction): O’2 OH’ H2O2 OH’

35. Reactive oxygen metabolites are particularly useful in eliminating microbial organisms that grow within phagocytes e.g.M.tuberculosis,Histoplasma capsulatum .

36. Some agents released from the granules of phagocytic cells do not require oxygen for bactericidal activity. These include lysosomal hydrolases ,permeability increasing factors,defensins and cationic proteins. 2.Oxygen-independent bactericidal mechanism

37. In addition to oxygen dependent and oxygen –independent mechanisms, recently role of nitric oxide(NO)in inflammatory reaction has been emphasised.NO is produced by endothelial cells as well as by activated macrophages .In experimental animals, NO has been shown to have fungicidal and anti-parasitic action but its role in bactericidal activity in human beings is yet not clear. 3.Nitric oxide mechanism .

38. Metchnikoff’s phagocytosis theory was less an explanation of host defence than a proposal that might account for establishing and maintaining organismal ‘harmony’. By tracing the phagocyte’s various functions through phylogeny, he recognized that eating the tadpole’s tail and killing bacteria was the same fundamental process: preserving the integrity, and, in some cases, defining the identity of the organism . Metchnikoff theory

39. Metchnikoff was fundamentally correct in recognizing the unity of the role of the phagocyte in cellular turnover and in host defence. Phagocytes have clearly been shown to have a role in immunity against bacteria, fungi and viruses, but,more recently, the mechanisms by which they continuously monitor cell viability have been elucidated. Metchnikoff conceived that host defence was only a more specialized case of determining self and non-self..

40. The phagocyte addressed both arms of this fundamental question — namely, an ability to recognize ‘self’ and ‘other’, and then a capacity to rid the organism of the unwanted foreign matter.These capabilities evolved from its earliest function as a nutritive cell, by which it discerned host and foreign substances, eating the latter and ignoring the former. So, in simple animals,‘eating ’ is the most primitive expression of the more general capability of a selective ‘attack’ apparatus The basic characteristics of the phagocyte were adapted in animals with a gut into a different form of ‘eating’. In these higher animals, the nutritive function is displaced, and the rudimentary capacities of recognition and destruction are directed both to foreign invaders (pathogens) and to host elements that have become ‘foreign’— that is, they are damaged or dying.

41. These are also called permeability factors or endogenous mediators of increased vascular permeability ,these are a large and increasing number of endogenous compounds which can enhance vascular permeability .However ,currently many chemical mediators have been identified which partake in other processes of acute inflammation as well such as CHEMICAL MEDIATORS OF INFLAMMMATION

42. E.g. vasodilation,chemotaxis,fever ,pain and cause tissue damage. The substances acting as chemical mediators of inflammation may be released from the cells ,the plasma,or damaged tissue itself. They are broadly classified into 2 groups : 1. mediators released by cells 2. mediators originating from plasma

43. Cell-derived mediators .1.Vasoactive Amines Two important pharmocologically active amines that have role in the early inflammatory response(first 1 hour) are histamine and 5-hydroxytryptamine(5-HT) or serotonin 1.Histamine- it is stored in the granules of mast cells , basophills , and platelets. Histamine is released from these cells by various agents like:

44. Stimuli or substances inducing acute inflammation, anaphylotoxins , neuropeptides, interlukins . 2.Arachidonic acid metabolites Source-diet directly Conversion of essential fatty acid, linoleic acid to arachidonic acid.

45. The name pg was first given to a substance found in human seminal fluid but now the same substance has been isolated from a number of other body tissues. Pg’s and related compounds are also called “autacoids”.

46. Metabolites via cyclo oxygenase pathway A) prostaglandins( PGD2,PGE2,PGF- ) B) thromboxane A2 C) prostacyclin (PGI2) Metabolites via lipo-oxygenase pathway(5-HETE,leukotrines A) 5HETE-which is potent chemotactic agent for neutrophils B) Leukotrines or slow reacting substances of anaphylaxis (SRS-As) are so named as they were first isolated from leucocytes.

47. Firstly unstable,leukotreine A4(LTA4) is formed which is acted upon by enzymes to form LTB4( chemotactic for phagocytic cells and stimulates phagocytic cell adherence ) while LTC4, LTD4 and LTE4 have common actions by causing smooth muscle contraction and thereby induce vasoconstriction ,bronchoconstriction and increased vascular permeability.

48. 3. Lysosomal Components The inflammatory cells – neutrophils and monocytes ,contain lysosomal granules which on release elaborate a variety of mediators of inflammation.:- Granules of neutrophils- These are two types: Specific or secondary,and azurophil or primary.The specific granules contain lactoferrin,lysozyme,alkaline phosphatase and collegenase while large azurophil granules have myeloperoxidase ,acid hydrolases and neutral proteases such as elastase,collegenase and proteinase

49. Acid proteases act within the cell to cause destruction of bacteria in phagolysosome while neutral proteases attack on extracellular constituents such as basement membrane,collagen,elastin,cartilage etc.

50. Granules of monocytes and tissue macrophages These cells on degranulation also release mediators of inflammation like acid proteases , collegenases,elastase and plasminogen activator. 4.Platelet activation factor (PAF) Helps in increased vascular permeability Bronchoconstriction Chemotaxis

51. 5.CYTOKINES Cytokines are polypeptide substances produced by activated lymphocytes ( lymphokines ) and activated monocytes( monokines ).These agents may act on ‘self’ cells producing them or on other cell. Currently main cytokines acting as mediators of inflammation are interlukin-1,TNF α and β ,interferon- γ are produced by activated Tcells .

52. The chemokines include interlukin 8 and platelet factor-4 from activated platelets,both of which are potent chemoattractant for inflammatory cells and hence their name. If- γ causes activation of macrophages and neutrophils and is associated with synthesis of nictric acid synthase. Chemokines are 1. IL-8 chemotactic for neutrophil Platelet factor 4 chemotactic for neutrophils monocytes and eosinophils MCP-1 chemotactic for monocytes Eotaxin chemotactic for eosinophils .

53. II.Plasma derived mediators( plasma proteases) 1.The kinin system Bradykinin acts in early stage of inflammation and its effect include Smooth muscle contraction Vasodilation Increased vascular permeability Pain.

54. 2.The clotting system: Increased vascular permeability Chemotaxis for leucocyte Anticoagulant activity 3.The fibrinolytic system This system is activated by plasminogen activator.it causes activation of factor XII to generate bradykinin Splits off complement c3 to form c3a which is permeability factor.

55. 4. The complement system Complement system on activation by classic pathway or alternate pathway yields anaphylatoxins which cause Release of histamine Increased vascular permeability C3b augments phagocytosis

56. Phagocytosis is a specific form of endocytosis by which cells internalise solid matter, including microbial pathogens. While most cells are capable of phagocytosis , it is the professional phagocytes of the immune system, including macrophages , neutrophils and immature dendritic cells, that truly excel in this process. Phagocytosis is one of the most important processes in cellular events occuring in inflammation thus helping in the body defense mechanism to eliminate or limit the spread of injurious agent as well as to remove the consequent necrosed cells and tissues.. CONCLUSION

57. Text book of pathology-Harsh Mohan, 4 th edition Pathologic basis of disease- Robbins&Cotran ,8 th edition Internet REFERRENCES

58. THANK YOU

59. GOOD MORNING

60. Innate immunity , or nonspecific, immunity is the natural resistance with which a person is born. It provides resistance through several physical, chemical, and cellular approaches. Adaptive immunity  is often sub-divided into two major types depending on how the immunity was introduced

61. .   1 . Naturally accquired immunity  occurs through contact with a disease causing agent, when the contact was not deliberate, whereas  Artificially acquired immunity  develops only through deliberate actions such as vaccination. Passive immunity  is acquired through transfer of antibodies or activated T-cells from an immune host, and is short lived—usually lasting only a few months—whereas  active immunity  is induced in the host itself by antigen, and lasts much longer, sometimes life-long.

62. Defensins  are small arginine rich cationic proteins found in both vertebrates and invertebrates. They have also been reported in plants. They are, and function as host defence peptides. They are active against bacteria,fungi  and many enveloped and non enveloped viruses .They consist of 18-45 amino acids.

63. Cells of the immune system contain these peptides to assist in killing  phagocytosed bacteria, for example in  neutrophil granulocytes and almost all epithelial cells.Most defensins function by binding to the microbial cell membrane and, once embedded, forming pore-like membrane defects that allow efflux of essential ions and nutrients

64. The alpha defensnis  peptides are increased in chronic inflammatory conditions. increased in several cancers, including colorectal cancer. An imbalance of defensins in the skin may contribute to acne. Defensins are found in the human skin during inflammatory conditions like psoriasis and also during wound healing

65. THANK YOU